Homopolar Welding for J-Lay Pipeline Construction

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Homopolar Welding (HPW) is a high speed electric resistance forge welding process being developed for single shot girth welds proposed for the J-Lay pipelaying technique in deepwater. The homopolar welding technique uses the high amperage direct cmTent output from homopolar generators to produce localized heating at the pipe interface, completing a weld in under five seconds regardless of pipe diameter or wall thickness. During the most recent welding research program, homopolar pipe welding technology made substantial advances in the process using a laboratory fixture to join small diameter HSLA steel linepipe (3-inch Schedule 80). Specific improvements on two high strength linepipe steels (X60 & X65) include increased impact toughness to near base metal values, improved weld profile, near base metal microstructure at the weld, and reduced generator requirements. Based on these improvements, a new welding fixture was designed and built capable of joining 12 inch schedule 60 steel linepipe. Work is underway to adjust the operation of the new welding fixture to match the performance of the 3 inch welding fixture. Seven welds have been completed, all having base metal yield and tensile strengths and ductility. The paper will cover homopolar welding basics and the recently completed pipe welding research program, emphasizing the mechanical properties of welds and the robustness of the process.